Electrolytically treating scrap-tin.



' irnn STAT PATENT ()FFICTE.

EDIVARD D. KENDALL, OF NEW YORK, N. Y.

l ELECTROLYTlCALLY TREATING SCRAP-TIN.

SPECIFICATION forming part of Letters Patent No. 656,982, dated August28, 1900.

Application filed November 20, 1899. Serial No. 737,676. (No specimens.)

To all whom it may concern;

Be it known that I, EDWARD D. KENDALL, of the city and State of NewYork, have invented certain Improvements in Processes ofElectrolytically Treating Scrap-Tin for the Separate Recovery of PureIron and Tin Therefrom, of which the following isa specification.

In the processes for recovering the tin from so-called scrap tin-plateheretofore commonl y employed the iron residuum. is of comparativelysmall value,because itis not wholly freed from tin.

The principal objects of the electrolytic process herein described areto effect the complete dissociation and separate recovery of the ironand tin present in scrap tin-plate and, incidentally, to secure incommercial quanti ties as a by-product a nitrate of the alkali metal oralkalineearth metal the nitrate of which forms the base of theelectrolyte employed. Commercial nitrate of sodium, commonly calledChili saltpeter is preferably employed because of its comparativelysmall cost; but there may be employed nitrate of potassium or ammoniumor calcium or any other suitable nitrate, it being understood that anitrate which in aqueous solution, under the influence of the electriccurrent, would deposit on thecathode any metal other than tin would notbe a suitable nitrate for the present purpose.

In carrying the invention into practice there is prepared an electrolyteconsisting of an aqueous solution containing five per cent, more orless, by weight, of the nitrate selected. The solution is usuallyfiltered and is then introduced into an electrolytic vat,which may haveany desired form or size and may be made of iron or steel or of wood.The inner surface of the vat, which is exposed to contact with thesolution, may, if desired, be lined with metal or coated with asphalt orsuitable paint or other chemical-resisting material. In appropriaterelation to the electrolyte and in any d esired position or positionsthere may be arranged a plate or plates of carbon or of tin or othermetal coated with tin to serve as the cathode. It will be understoodthat if the vat be made of metal or lined with metal such metal may insome instances be advan 'tageously made to serve as the cathode,particularly if the surfaces in contact with the electrolyte be coatedwith tin. The scrap tinplate to be operated upon, which may or may nothave been passed through corrugatingrolls, is loosely packed to form amass, which is submerged in the electrolyte and made to serve as theanode by connection in the usual manner with one terminal of achargedelectric circuit,the cathode being electrically connected with the otherterminal of said circuit. Of course a plurality of so-preparedelectrolytic vats, preferably arranged in series, may be operatedtogether. The ensuing chemical action is as follows:Sn-I-NaNO,-l-H,O=Sn0 +NaNO +H The results are the formation of stannicoxid in the form of a solid precipitate, a portion of which on coming incontact with the cathode will be reduced to metallic tin. A furtherresult is the reduction to a nitrite of the sodium nitrate or othernitrate originally contained in the electrolyte. After using theelectrolyte until it ceases to act with the desired energy I add enoughof the nitrate (say sodium nitrate) to restore efficiency to thesolution. By such repeated. addition the solution finally becomesheavily charged with sodium nitrite and usually contains a smallproportionate quantity of unchanged nitrate and also some ammoniaresulting from the electrolytic decomposition of the nitrite. It mayalso contain traces of tin, which may be recovered by electrolysis whendeemed expedient. This strong solution of sodium nitrite is conducted toany suitable evaporating plant in which the water present is driven off,leaving as a residuum the salts from the solution in a solid formavailable for use as asource of nitrogen in the preparation ofagricultural fertilizers.

Should the electrolytic operation have been carried so far as to havegenerated in the solution a material quantity of ammonia, this may beneutralized with an equivalent quantity of sulfuric acid, in which casethe saline mass recovered from the solution will contain some ammoniasulfate, also useful for fertilizing purposes.

The stannic oxid, which forms a precipitate in the electrolyte, and anymetallic tin which may have been produced may be from time to timecollected and utilized in any of the usual Ways for the production ofsodium stannate or metallic tin.

It will be understood that the treatment is more or less prolongedaccording to the greater or less size of the mass of scrap-tin submergedin the electrolyte, until the tin and iron present are completelydissociated. The sodium nitrate employed as herein set forth is soeffective an electrolytic agent that the component metals of scraptinplate can be completely separated within thirty minutes by the use ofa six-volt electric current of adequate amperage.

The advantages of the described electrolytic treatment of scraptin-plate are threefold-to wit: first, the complete separation of thetin and the production of a pure iron having the same commercial valueas like grades of iron uncontaminated with tin;

secondly, the absence of any evolution from' the electrolyte of anynoxious or deleterious gases, and, finally, the opportunity afforded forthe recovery of a valuable by-p'roduc't to wit, the described nitriteavailable in the manufacture of agricultural fertilizers. What isclaimed as the invention is 1. The improvement in the art trelefctrolytically dissociating the iron and tin of socalled scraptin-plate, which consists in the preparation of an electrolyte composedof an aqueous solution of a nitrate of an alkali metal, or a nitrate ofan alkaline-earth metal the introduction into said electrolyte of ananode 'consistin g of .a mass'of scrap tin-plate;

the electrical connection of said mass with one terminal of a chargedelectric circuit and i the establishment in contact with said elec- Itrolyte, of a suitable cathodeelectricallyconnected with the otherterminal'of'said charged electric circuit.

2. The improvement in the electrolytic treatment of scrap tin-plate,which consists in the preparation of an electrolyte composed of anaqueous solution of a nitrate of an alkali metal, or a nitrate of analkaline-earth metal; the introduction into said electrolyte 3 of ananode consisting of a mass of scrap tinwhich consists in submerging ananode composed of said scrap tin-plate in an electrolyte composed of anaqueous solution of a nitrate of an alkali metal or anitrate of analkalineearth metal 5 the electrical connection of said anode with oneterminal of acharged electric circuit; the establishment of a suitablecathode electrically connected with the other terminal of said chargedelectric circuit Whereby the nitrate originally present is transformedinto a nitrite; the addition of sodium or other nitrate to the solutionfrom time to time as required, and finally, the collection I andevaporation of the resulting strong solutioP for the recovery of thesalt therefrom in a solid form.

4. In the electrolytic treatment of scrap tinplate, consisting in thesubmergence of an anode composed of scrap tin-plate in an electrolytecomposed of an aqueous solution of sodium or other suitable nitrate, andin contact with a suitable cathode, the said anode and cathodeelectrically connected respectivel'y with the opposite terminals of acharged 'electric circuit; the introduction into the said electrolytefrom time to time, as required, of additional quantities of said sodiumor other hitrate, ah'd the concentration by evaporation of theresulting'strong solution for the recovery of the nitrite therefrom.

EDWAR D. KENDALL. Witnesses:

' A. M. JONES,

E. GATTERER.

